The present invention relates to time determination circuits for cameras such as automatic exposure cameras. More particularly, the invention relates to a power maintaining time determination circuit.
A conventional power maintaining time determination circuit is so designed that the power is maintained on for twenty to thirty seconds after the photographer has depressed the release button halfway to turn on the power switch to thereby use the available battery power conservatively. During this period, the photographer determines the exposure, focusing and the composition conditions after which he operates the shutter release. The power maintaining time determination circuit is provided independently of other circuits such as the shutter control circuit and the display circuit.
The conventional power maintaining time determination circuit is disadvantageous in that if the photographing operation is completed prior to the expiration of twenty to thirty seconds, the circuit still maintains the power on even though it is no longer needed thereby wasting battery energy. Moreover, as the power maintaining time determination circuit is provided separately from other circuits as described above, the number of components needed for the electronics in the camera is great and it is difficult to economically use the limited space in the camera which results in a high manufacturing cost. It is difficult to provide a capacitor for time determination in the form of an integrated circuit even using present IC techniques. Accordingly, the conventional time determination circuit suffers from problems which cannot be solved through known IC techniques.